While specific definitions of LEO vary between sources, LEO is generally considered to include any orbital path having a locus within about 2,000 kilometers (km) of the Earth's surface. A typical LEO satellite, for example, follows a circular orbital path between about 200 km and about 1,000 km above the Earth's surface. Many LEO satellites travel at about 27,400 km/h (8 km/s) and complete an orbit, or revolution, around the Earth approximately every 90 minutes. To its advantage, less energy is required to propel a satellite from the Earth's surface onto LEO than onto a higher orbit, and LEO communication satellites require less powerful amplifiers for successful transmission of data to the Earth's surface. As a consequence, the lower radiation levels associated with LEO communication satellites permit the use of less robust, and thus less costly, satellite components.
Medium-earth-orbit (MEO), which is sometimes also referred to as an intermediate circular orbit (ICO), is generally considered to include any orbital path having a locus further from the Earth's surface than LEO and less distant than geostationary orbit (GEO) levels. For reference, GEO satellites typically travel at an altitude of about 35,786 km above the Earth's surface and have an orbital period equal to one sidereal day.